This disclosure relates to content identification.
Content of a first type, such as web pages, can be identified by one or more content servers in response to queries. The queries can, for example, include search engine queries. Additional contents of a second type, such as advertisements, can also be identified in response to the queries. For example, advertisements can be identified based on keywords in the queries.
Occasionally, however, content of the second type may not be identified in response to the query, or the identified content of the second type defines a small content set.